JP2005268508A - Ceramic thin film capacitor and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a ceramic thin film capacitor not required for being exposed to an electrode at high temperature. <P>SOLUTION: The method for manufacturing a ceramic thin film capacitor 1 has the step of exposing a non-sintered ceramic film 3 under laser irradiation to be sintered for forming a ceramic dielectric layer 2, and the ceramic thin film capacitor 1 has such a structure that the ceramic dielectric layer 2 is pinched between a pair of electrodes 4 and 5. More specifically, this method further comprises the steps of (A) coating a ceramic paste on a lower electrode 4, and next drying the coated paste, thereby forming the non-sintered ceramic film 3 on the lower electrode 4; (B) exposing the non-sintered ceramic film 3 under laser irradiation to be sintered for forming the ceramic dielectric layer 2; and (C) forming an upper electrode 5 on the ceramic dielectric layer 2. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a ceramic thin film capacitor and a method for manufacturing the same.

In recent years, electronic devices have been required to be smaller and thinner. Many electronic devices use circuit boards on which electronic components such as ICs and capacitors are mounted, and these circuit boards are also required to be small and thin. For this reason, the capacitor mounted on the surface of the substrate is formed inside the substrate. A thin film capacitor is formed as a capacitor for this purpose. As a conventional method of manufacturing a thin film capacitor, for example, a ceramic paste is applied to the surface of the lower electrode, dried, and then sintered at 800 ° C. or higher to form a ceramic dielectric layer. The method of forming is mentioned (patent document 1).
JP 2000-243137 A

  However, at a high temperature of 800 ° C. or higher, the lower electrode is likely to be oxidized or melted. Therefore, there are concerns that an excellent capacitor cannot be formed by the conventional manufacturing method, and that there is very little room for selecting a material for the lower electrode. An object of this invention is to provide the manufacturing method of the ceramic thin film capacitor which does not require exposing an electrode to high temperature. In addition, an object of the present invention is to provide a ceramic thin film capacitor having a novel configuration that can be manufactured by such a manufacturing method.

As a result of intensive studies on the sintering behavior of oxide particles, the present inventors have found a means for sintering ceramics to such an extent that they can be used as capacitors without being exposed to high temperatures, and have the following characteristics: The present invention has been completed.
(1) A method of manufacturing a ceramic thin film capacitor having a structure in which a ceramic dielectric layer is sandwiched between a pair of electrodes, and the ceramic dielectric layer is formed by sintering an unsintered ceramic film by subjecting it to laser irradiation. A method for manufacturing a ceramic thin film capacitor, comprising the step of:
(2) The production method according to (1) above, comprising the following steps (A) to (C).
(A) A step of forming a non-sintered ceramic film on the lower electrode by applying a ceramic paste on the lower electrode and then drying the applied paste.
(B) A step of sintering the unsintered ceramic film by subjecting it to laser irradiation to form a ceramic dielectric layer.
(C) A step of forming an upper electrode on the ceramic dielectric layer.
(3) The manufacturing method according to (2), wherein, in the step (B), laser irradiation is performed so as to produce irregularities on the surface of the obtained ceramic dielectric layer.
(4) The (2) or (3) above, wherein in the step (B), the ceramic ceramic layer is patterned by subjecting the unsintered ceramic film to partial laser irradiation. The manufacturing method as described.
(5) The manufacturing method according to any one of (1) to (4), further including a step of impregnating the ceramic dielectric layer with a resin.
(6) The ceramic thin film capacitor is mounted on a printed circuit board, and an unsintered ceramic film is formed on the printed circuit board to be mounted, and the unfired ceramic board formed on the printed circuit board is formed. The manufacturing method according to any one of (1) to (5) above, wherein the sintered ceramic film is subjected to laser irradiation.
(7) A ceramic thin film capacitor having a structure in which a ceramic dielectric layer is sandwiched between a pair of electrodes, wherein at least one main surface of the ceramic dielectric layer has irregularities.

According to the method for manufacturing a ceramic thin film capacitor of the present invention, the fear of oxidation and melting of the lower electrode in the process of obtaining the ceramic dielectric layer by sintering is remarkably reduced.
In a preferred embodiment of the present invention, irregularities can be formed on at least one main surface of the ceramic dielectric layer. The ceramic thin film capacitor of the present invention thus obtained has a large capacitance.
In a preferred embodiment of the present invention, a desired pattern can be formed or a capacitor having a desired area can be manufactured by partially irradiating a laser.
In a preferred embodiment of the present invention, flexibility can be imparted to the ceramic thin film capacitor by impregnating the sintered ceramic dielectric layer with resin.
In a preferred aspect of the present invention, sintering for manufacturing a ceramic thin film capacitor can be performed on the substrate without heating the entire printed circuit board. It can be realized at the same time.

  A ceramic thin film capacitor, which is an object of the manufacturing method of the present invention, is a capacitor having a structure in which a ceramic dielectric layer is sandwiched between a pair of electrodes. The ceramic dielectric layer is not particularly limited as long as it is a layer made of a sintered metal oxide as an insulator, and is preferably a layer made of a sintered metal oxide exhibiting ferroelectricity. The material and structure of a pair of electrodes sandwiching the ceramic dielectric layer can appropriately adopt the material and structure of electrodes of known electronic components. A feature of the manufacturing method of the present invention is that an unsintered ceramic film is subjected to laser irradiation as a sintering means for obtaining a ceramic dielectric layer.

  An unsintered ceramic film is a film containing unsintered metal oxide particles, and even if an organic resin or the like exists as a so-called binder between the metal oxide particles in order to maintain the structure of the film. Alternatively, the film may be formed with weak bonds such that the metal oxide particles do not sinter due to heat. Sintering means that metal oxide particles constituting an unsintered ceramic film are strongly bonded to each other mainly by a solid phase reaction to form an integral structure (ceramics). Unlike the conventional sintering by heating, the laser irradiation allows the energy for sintering the metal oxide particles to be concentrated only in a desired portion. For this reason, not only the undesirable reaction of the metal constituting the capacitor electrode can be reduced, but also the portion to be sintered can be patterned.

  In the manufacturing method of the present invention, energy for sintering can be locally provided by laser irradiation. Therefore, when the manufactured ceramic thin film capacitor is to be mounted on a printed circuit board, It is also possible to form a sintered ceramic film on a printed circuit board to be mounted, and subject the unsintered ceramic film formed on the wired circuit board to laser irradiation. If a ceramic thin film capacitor is manufactured on a printed circuit board in this way, the process of mounting a separately manufactured capacitor on the printed circuit board as in the past can be omitted, and defects due to mounting errors can be significantly reduced. it can. Here, forming an unsintered ceramic film on the printed circuit board includes forming an unsintered ceramic film on the wired circuit board via an electrode for a ceramic thin film capacitor.

  Hereinafter, although the process of the preferable form of this invention is demonstrated in order, this invention is not restricted to the specific process described below, The process of sintering by using an unsintered ceramic film | membrane for laser irradiation The manufacturing method of the ceramic thin film capacitor containing is included widely. The preferable form of this invention has the process of the above-mentioned (A)-(C). FIG. 1 is a diagram schematically showing the production method of the present invention. Hereinafter, the preferred production method of the present invention will be described in more detail with reference to FIG.

(A) A step of applying a ceramic paste on the lower electrode and then drying the applied paste to form an unsintered ceramic film on the lower electrode (FIG. 1 (a)):
The lower electrode 4 is one of a pair of electrodes constituting the ceramic thin film capacitor 1. For convenience of description, in this specification, the vertical direction is described so as to form a layer from the bottom to the top as the process proceeds, but the description regarding such a direction does not specify the mounting direction or the direction in use. Absent. The lower electrode 4 is not particularly limited as long as it can be used as an electrode of an electronic component, and is generally a metal foil, preferably a copper foil or a nickel foil. A thin film of copper or nickel formed on the insulating substrate by sputtering or plating may be used as the lower electrode 4. From the viewpoint of mechanical strength and electrical resistance, the thickness of the lower electrode 4 is preferably 9 to 35 μm, more preferably 18 to 35 μm.

  FIG. 2 is a cross-sectional view of an example of a ceramic thin film capacitor manufactured by the present invention. When the ceramic thin film capacitor 1 manufactured according to the present invention is mounted on the wiring circuit board 6 as shown in FIG. 2, the lower electrode 4 is formed on the insulating layer (not shown) of the wiring circuit board 6. May be. In this case, as the insulating layer, a layer made of an insulating material that can be used for the printed circuit board can be taken in as appropriate, and a layer made of polyimide or polyester is exemplified.

  The ceramic paste applied on the lower electrode 4 includes at least unsintered particles (hereinafter also referred to as “ceramic particles”) that can form ceramics by sintering, and a solvent. In consideration of dispersion, stability of the obtained ceramic film, and the like, it preferably further contains a resin serving as a binder, a plasticizer, and the like.

  The ceramic particles can be used without particular limitation as long as they are inorganic particles capable of forming ceramics by sintering, and generally include metal oxide particles, preferably metal oxide particles exhibiting ferroelectricity. It is done. Examples of the metal oxide particles preferably used include titanate, zirconate, stannate, silicate, titanium oxide, and alumina. From the viewpoint of high dielectric constant and easy availability, titanate and zirconate. Salt and the like are preferable. Specific examples of titanates include strontium titanate, barium titanate, calcium titanate, magnesium titanate, zinc titanate, lanthanum titanate, neodymium titanate, lead titanate, barium zirconate titanate, titanium zirconate Lead acid, barium strontium titanate and the like can be mentioned, and barium titanate, barium zirconate titanate and the like are preferable. Specific examples of the zirconate include barium zirconate titanate, lead zirconate titanate, barium zirconate, calcium zirconate, lead zirconate and the like. Examples of the stannate include barium stannate and calcium stannate. Examples of the silicate include magnesium silicate.

  The shape and size of the ceramic particles used in the present invention are not particularly limited, and commonly used ceramic particles may be used as they are. From the viewpoint of miniaturization and thinning of the obtained capacitor and ease of sintering by laser, the volume average particle diameter of the ceramic particles is preferably 0.05 to 1 μm. The volume average particle diameter of the ceramic particles can be obtained from a diffraction pattern when a laser is applied to a dilute suspension of ceramic particles, and such measurement is performed by LA-750 manufactured by Horiba, Ltd.

  The solvent of the ceramic paste is not particularly limited as long as it is a liquid at room temperature and has a boiling point of about 60 to 200 ° C., may be water or an organic solvent, or a mixed system thereof. It may be. Examples of the organic solvent include polar solvents such as alcohol. Solvent selection criteria include dissolving binders and plasticizers described below, and wettability to ceramic particles.

  Preferably, the ceramic paste used in the present invention contains a resin as a binder in a solution state. Conventionally known resins can be appropriately used as the binder. Examples of water-based binders include methylcellulose, hydroxypropylmethylcellulose, carboxymethylcellulose, hydroxymethylcellulose, starch, polyvinyl alcohol, polyethylene oxide, sodium polyacrylate, and polyacrylamide. Dispersibility, stability, and compatibility with water From these, carboxymethylcellulose, polyvinyl alcohol and the like are preferable. Examples of the non-aqueous binder include polyethylene, polypropylene, ethylene-vinyl acetate copolymer, polystyrene, acrylic resin, polyamide resin, polyvinyl butyral, and the like, and polyvinyl butyral is preferable from the viewpoint of sheet moldability.

  Preferably, the ceramic paste used in the present invention contains a plasticizer. Examples of the plasticizer include glycerin, polyethylene glycol, dibutyl phthalate, and trioctyl trimellitate.

  For specific preparation of the ceramic paste, known techniques may be referred to as appropriate, and specific examples thereof are described in Patent Document 1.

  The means for applying the ceramic paste onto the lower electrode 4 is not particularly limited, and a conventionally known coating technique can be appropriately adopted according to the viscosity of the ceramic paste. Examples of such a coating technique include a casting method using a doctor blade.

  The drying after the coating of the ceramic paste has only to evaporate the solvent to such an extent that the shape as a coating film can be maintained, and the specific means and conditions are not particularly limited. Specific examples of drying include leaving at 80 to 180 ° C. for 1 to 30 minutes. At this time, the binder may be removed by heat treatment for several hours in a vacuum or nitrogen atmosphere. The conditions for removing the binder can be appropriately determined according to the type and amount of the binder. As described above, the unsintered ceramic film 3 can be formed on the lower electrode 4.

(B) A step of sintering an unsintered ceramic film by subjecting it to laser irradiation to form a ceramic dielectric layer:
In the present invention, energy is supplied by irradiating the unsintered ceramic film 3 with laser light, and the ceramic particles constituting the unsintered ceramic film 3 are sintered. For this reason, unlike the conventional case where the entire lower electrode 4 is heated to a high temperature, it is possible to remarkably reduce the undesirable energy imparted to the lower electrode 4 during ceramic sintering. In particular, when the unsintered ceramic film 3 is formed on the printed circuit board, energy can be supplied only to the ceramic particles and the vicinity thereof without applying energy to the printed circuit board itself.

In the present invention, a conventionally known laser can be used without any particular limitation. Specific examples include an ArF excimer laser, a KrF excimer laser, a carbonic acid laser, a green laser (visible light), a YAG laser, and a UVYAG laser. The wavelength of the laser is not particularly limited, and is preferably 190 to 3000 nm. The laser irradiation may be sufficient to sinter the ceramic, and examples thereof include 1 to 100 shots at an energy density of 50 to 250 mJ / cm ² . At this time, the pulse width is preferably 20 to 80 nsec.

  Preferably, the laser is irradiated so as to generate irregularities on the surface of the obtained ceramic dielectric layer 2. The surface of the ceramic dielectric layer 2 may be one main surface of the dielectric layer 2, but is usually a surface facing the lower electrode 4. Protruding irregularities on the surface of the ceramic dielectric layer can be easily realized by increasing the laser energy density or extending the irradiation time. The unevenness of the obtained ceramic dielectric layer 2 preferably has a maximum roughness (Rmax) of 1 to 20 μm that can be measured with a non-contact optical surface roughness meter. By providing irregularities on the surface of the ceramic dielectric layer 2 in this way, the surface area of the dielectric layer increases, so that the capacitance of the capacitor can be increased without increasing the size of the ceramic thin film capacitor 1 as a whole. .

  In this step, the entire surface of the unsintered ceramic film 3 may be subjected to laser irradiation to be fully sintered, or the unsintered ceramic film 3 may be partially subjected to laser irradiation. By controlling which part of the unsintered ceramic film 3 is subjected to laser irradiation, only a desired part of the unsintered ceramic film 3 can be sintered. In other words, the ceramic dielectric layer 2 (patterned ceramic dielectric layer 2) having a desired pattern can be formed. At this time, a portion of the unsintered ceramic film 3 that has not been subjected to laser irradiation remains as an insulating layer (FIG. 1B). In order to control laser irradiation, known laser-related techniques can be adopted as appropriate, and examples of such techniques include techniques for scanning and scanning lasers and techniques for using apertures that change the shape of lasers. .

  The ceramic dielectric layer 2 thus obtained is usually porous. For the purpose of imparting flexibility and strength to such a ceramic dielectric layer 2, the voids of the dielectric layer 2 may be impregnated with a resin such as epoxy resin or polyimide (not shown). The impregnation method is not particularly limited, and there are a method of filling a hot-melt resin, a method of removing a solvent after filling a solution-like resin, and the like.

The size and shape of the ceramic dielectric layer 2 thus obtained is not particularly limited, and can be set as appropriate so as to satisfy desired electrical and mechanical requirements. From the viewpoint of the capacitor capacity and the mechanical strength of the dielectric layer, the thickness of the ceramic dielectric layer 2 is preferably 10 to 100 μm, and the cross-sectional area perpendicular to the thickness direction of the dielectric layer is preferably 0.04. is 25 mm ^2, the cross-section perpendicular to the thickness direction of the dielectric layer is preferably a rectangular or square shape, the length of one side thereof is preferably about 0.2 to 5 mm.

(C) A step of forming an upper electrode on the ceramic dielectric layer (FIG. 1C):
The upper electrode 5 is an electrode formed so as to be paired with the lower electrode 4 and sandwich the ceramic dielectric layer 2. Similarly to the lower electrode 4, the upper electrode 5 is not particularly limited as long as it can be used as an electrode of an electronic component, and is generally a metal thin film, and as a metal therefor, copper, nickel, gold, platinum, etc. Is exemplified. The method for forming the upper electrode 5 is not particularly limited, and may be a vapor deposition method such as sputter vapor deposition or a plating method. From the viewpoint of film strength and electrical resistance, the thickness of the upper electrode 5 is preferably 0.05 to 20 μm.

  When the ceramic dielectric layer 2 patterned by partially subjecting the unsintered ceramic film 3 to laser irradiation in the step (B) is obtained, the same as the patterned ceramic dielectric layer 2 The upper electrode 5 is preferably formed in a pattern. Examples of means for patterning the upper electrode 5 in this manner include a subtractive method and an additive method that are generally used for processing of a printed circuit board. More specifically, the subtractive method is described. After a metal thin film is formed on the entire surface of the ceramic dielectric layer 2 and the unsintered ceramic film 3 (FIG. 1C), an etching resist having a predetermined pattern is formed using a photoresist. It is formed on a metal thin film (not shown). Next, the patterned upper electrode 5 can be formed by etching the portion of the metal thin film not covered with the etching resist with an etching solution and removing the etching resist (FIG. 1D). At this time, the same method may be taken to pattern the lower electrode 4 (FIG. 1E).

  EXAMPLES Hereinafter, although this invention is demonstrated in more detail using an Example, these examples do not limit this invention at all.

(Example 1)
A ceramic paste was applied on copper foil 4 (thickness 35 μm, length 250 mm × width 250 mm) with an applicator, dried at 100 ° C. for 2 minutes, then at 150 ° C. for 30 minutes, and further at 400 ° C. in a nitrogen atmosphere. The binder was removed by heating for 2 hours to form an unsintered ceramic film 3 (FIG. 1A). The ceramic paste includes the following.
Ceramic particles: Sakai Chemical Barium Titanate (volume average particle size: 0.5 μm)
50 parts by weight,
Solvent: 8.8 parts by weight of a solvent obtained by mixing α-terpineol and diethylene glycol mono-n-butyl ether acetate at 9: 1 (weight ratio),
Binder: 17.5 parts by weight of polyvinyl butyral
Plasticizer: Trioctyl trimellitate 2 parts by weight.

The obtained unsintered ceramic film 3 was irradiated with a KrF excimer laser (wavelength 248 nm, pulse width 20 nsec) with an energy density of 250 mJ / cm ² , a shot number 50 and a laser beam diameter of 1 mm. At that time, patterning was performed so that the irradiated portion was a square of 3.2 mm in length and 1.6 mm in width, and laser was irradiated so as to form 100 of the squares. The distance separating adjacent squares was 100 μm. The ceramic dielectric layer 2 (thickness 50 μm) was formed by laser irradiation so that the squares were aligned (FIG. 1B). When the surface of the obtained ceramic dielectric layer 2 (surface facing the copper foil 4) was measured with a non-contact optical surface roughness meter (NT3000 manufactured by WYKO), Rmax was 1 μm.

  The obtained ceramic dielectric layer 2 was impregnated with a methyl ethyl ketone solution (40 wt%) of an epoxy resin. Then, the epoxy resin was hardened by drying at 100 degreeC for 5 minutes, and also leaving still at 150 degreeC for 30 minutes. Thereafter, copper was vapor-deposited to a thickness of 1 μm and etched into a square of 3.2 mm length × 1.6 mm width so as to match the pattern of the ceramic dielectric layer 2. This copper film is the upper electrode 5 (FIGS. 1C and 1D). Finally, the lower electrode 4 was also etched into a square of 3.2 mm length × 1.6 mm width to obtain a ceramic thin film capacitor 1 (FIG. 1E). The number of obtained ceramic thin film capacitors 1 was the same as the number of ceramic dielectric layers 2 of 3.2 mm length × 1.6 mm width obtained by patterning.

  The lower electrode 4 of the obtained ceramic thin film capacitor 1 was not damaged by oxidation. The relative dielectric constant ε at a frequency of 1 MHz of the ceramic dielectric layer 2 of this capacitor was 50, and the capacitance of the obtained capacitor was 100 pF.

(Comparative Example 1)
In the same manner as in Example 1, an unsintered ceramic film 3 was formed on the copper foil 4. Thereafter, the ceramic film 3 was sintered together with the copper foil 4 in the air at 900 ° C. for 2 hours. As a result, a ceramic dielectric layer 2 having a thickness of 50 μm was obtained. The surface of the obtained ceramic dielectric layer 2 was smooth and Rmax was 0.2 μm. Then, the upper electrode 5 was formed by vapor-depositing copper (thickness: 1 micrometer), and the ceramic thin film capacitor 1 was manufactured. The obtained ceramic thin film capacitor was cut into a square of 3.2 mm length × 1.6 mm width. This cut out capacitor was used as the capacitor of Comparative Example 1 and compared with the capacitor of Example 1 above. An oxide layer generated when the ceramic was sintered was formed on the lower electrode 4 of the capacitor of Comparative Example 1. The relative dielectric constant ε at a frequency of 1 MHz of the ceramic dielectric layer 2 of this capacitor was 50, and the capacitance of the obtained capacitor was 50 pF.

  Since the relative dielectric constant ε of Example 1 and Comparative Example 1 were equivalent, it was suggested that both Example 1 and Comparative Example 1 were sufficiently sintered. The reason why the capacitance of the capacitor of Example 1 was larger than that of the capacitor of Comparative Example 1 was that the surface area was increased due to the formation of irregularities on the surface of the ceramic dielectric layer 2 near the upper electrode 5 of the capacitor of Example 1. It is believed that there is.

It is a figure which represents the manufacturing method of this invention typically. As the process proceeds, the figure changes from (a) to (e). It is sectional drawing of an example of the ceramic thin film capacitor manufactured by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ceramic thin film capacitor 2 Ceramic dielectric layer 3 Unsintered ceramic film 4 Lower electrode 5 Upper electrode 6 Wiring circuit board

Claims (7)

  A method of manufacturing a ceramic thin film capacitor having a structure in which a ceramic dielectric layer is sandwiched between a pair of electrodes, comprising a step of forming a ceramic dielectric layer by sintering an unsintered ceramic film by subjecting it to laser irradiation. A method for producing a ceramic thin film capacitor. The manufacturing method of Claim 1 which has the process of following (A)-(C).
(A) A step of forming a non-sintered ceramic film on the lower electrode by applying a ceramic paste on the lower electrode and then drying the applied paste.
(B) A step of sintering the unsintered ceramic film by subjecting it to laser irradiation to form a ceramic dielectric layer.
(C) A step of forming an upper electrode on the ceramic dielectric layer.   3. The method according to claim 2, wherein, in the step (B), a laser is irradiated so as to produce irregularities on the surface of the obtained ceramic dielectric layer.   4. The manufacturing method according to claim 2, wherein the patterned ceramic dielectric layer is formed by partially subjecting the unsintered ceramic film to laser irradiation in the step (B).   Furthermore, the manufacturing method as described in any one of Claims 1-4 which has the process of impregnating the said ceramic dielectric material layer with resin.   The ceramic thin film capacitor is mounted on a wired circuit board, and an unsintered ceramic film is formed on the wired circuit board to be mounted, and the unsintered ceramic formed on the wired circuit board The manufacturing method according to any one of claims 1 to 5, wherein the film is subjected to laser irradiation.   A ceramic thin film capacitor having a structure in which a ceramic dielectric layer is sandwiched between a pair of electrodes, wherein at least one main surface of the ceramic dielectric layer is uneven.

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